1. Field of the Invention
The present invention relates to an improved bit-by-bit time-division digital switching network as described in U.S. Pat. No. 4,258,434.
2. Description of the Prior Art
According to the invention, a prior art bit-by-bit switching principle for single or component incoming channels which are multiplexed into incoming multiplex channels is retained. This principle relates chiefly to the correspondence of a predetermined-state bit in an incoming channel with the transmission of an outgoing channel address along an intermediate multiplex digital highway between the receiving part and the transmission part. At the transmission part, detection of the outgoing channel address word generates a bit in the predetermined state, and the absence of this detection generates a bit in the inverse state. These criteria apply for each recurrent frame of the multiple highway which transmits, by means of outgoing channels, address words the implicit binary state of same-rank bits in incoming channel words having a given number of bits. The means common to the switching networks in the present invention and in U.S. Pat. No. 4,258,434 are the following:
means for phasing the incoming digital channels;
means for storing bits having the same rank in the phased incoming channel data words;
means for detecting stored same rank bits having a predetermined binary state;
means for storing address words of the outgoing digital channels to be switched to the incoming digital channels;
means controlled by the predetermined binary state bit detecting means for reading stored outgoing channel address words corresponding to switched incoming channels with bits having the predetermined binary state and a same rank;
means for multiplexing the read outgoing channel address words into an address word multiplex digital highway at high rate;
means connected to the multiplex digital highway for detecting the address words of each outgoing digital channel; and
means controlled by the address word detecting means for delivering a bit having the predetermined binary state or the other binary state into said rank of a data word of the outgoing digital channel in response to the detection or failure of the detection of the address word of said outgoing digital channel.
In accordance with the U.S. Pat. No. 4,258,434, the number of address words which are conveyed in a recurrent frame of the intermediate multiplex highway is statistically equal at the most to half the number of incoming channels. If all the same rank bits of the words (or groups of bits) in the incoming channels are in the predetermined binary state, the highway frame is entirely filled with address words, equal in number to the number of incoming channels. If all the same rank bits of incoming channel words (or groups of bits) are in the other binary state, the highway frame does not contain any address words. Consequently, the sum of so-called free intervals which are available and adaptable for transmission of additional information (such as supervisory words); and which are included in the ends of frames in an intermediate highway multiframe, occupies a variable time period which lies between 0 and the number of the time intervals of address words which are capable of being transmitted in this multiframe.